The biggest winter storm of the season socked the Twin Cities on Thursday and Friday, creating some of the worst road conditions the Minnesota State Patrol has seen in 25 years.

Snow- and ice-covered roads were so treacherous, the State Patrol advised no travel unless absolutely necessary throughout much of the state this weekend.

"With the forecasted cold temperatures and current ice conditions, we anticipate a lot of problems on the roads for the next several days," State Patrol Lt. Col. Matt Langer said in a statement Friday.

The storm began as rain and sleet Thursday in some places, as temperatures hovered around freezing.

Traffic moved slowly on East Sevent Street and Mounds Boulevard on Friday February 21, 2014. (Pioneer Press: Jean Pieri)

A layer of wet, slushy snow turned to ice as temperatures fell overnight into the single digits, leading to dangerous roads, which saw more than 1,900 spinouts and 680 crashes -- 64 with injuries and one that resulted in a fatality, according to the State Patrol.

High temperatures in the teens and lows in the single digits below zero were expected for the metro area this weekend, with lower temperatures in store for next week, according to the National Weather Service.

The State Patrol closed southbound Interstate 35 from Owatonna to the Iowa border shortly after 1 a.m. Friday because of numerous accidents and stranded vehicles in the blizzard conditions. I-35 remained closed Friday night between Owatonna and Albert Lea before finally reopening by midnight.

Troopers dealt with scores of accidents, including a crash in Wabasha County, in which the driver of a van -- Leonard Kahn, 60, of Elgin -- was killed in a collision with a semi on ice-covered Minnesota 42. Additionally, 66 semis jackknifed statewide during the storm.

Although Interstate 94 remained open between Minneapolis and St. Paul, traffic was at a standstill during Friday morning's rush hour, as drivers tried to gain traction on the snow-covered ice.

According to the state Department of Public Safety, more than 250 people spent Thursday night in shelters across six Minnesota counties -- Steele, Freeborn, Renville, Le Sueur, Blue Earth and Cottonwood.

Gov. Mark Dayton issued an emergency executive order Friday, directing the Minnesota National Guard to assist stranded motorists across the state.

About 60,000 Xcel Energy customers lost power as a result of the storm. Nearly all had electricity restored by late Friday night, the utility said.

The storm also kept many children home for the day. Many Twin Cities schools closed, including the state's three largest districts: Anoka-Hennepin, St. Paul and Minneapolis.

The storm's snowfall total at the Minneapolis-St. Paul International Airport, the official weather observation point for the Twin Cities, was 9.9 inches. Until this storm, the biggest snowfall at the airport this season occurred Jan. 30, when 6.4 inches fell.

The recent snow only added to what has already been an above-average snowfall for the season. And much of that older snow has stuck around throughout the coldest winter since 1978-79, which is the eighth coldest on record in the Twin Cities.

At the airport, the snow depth Friday morning hit 24 inches -- topping the 23 inches on the ground after the Halloween Blizzard of 1991. One must look back to Jan. 26, 1982 to see that much snow on the ground.

The two-day snowfall brings this season's total to 57 inches -- 17.

5 more inches than what is considered normal at this point in winter and significantly more than the 31.3 inches seen at this point last winter.

The season's total also already has topped what is considered normal for annual snowfall: 54.4 inches.

Totals similar to the airport's were seen around the metro area on Friday. In downtown Minneapolis, weather service observers reported 10.5 inches and in North St. Paul, 10.1 inches. In Wisconsin, River Falls saw 11.5 inches and Clear Lake saw 12 inches.

Farther north, totals were even higher, with locations in Douglas County, Wis., seeing as much as 18 inches and spots in St. Louis County, Minn., seeing as much as 17.5 inches.

Both St. Paul and Minneapolis declared snow emergencies Thursday afternoon.

City plows in St. Paul were busy with residential streets Friday and would be back on arterial streets Saturday, said Dave Hunt, spokesman for the city's Department of Public Works.

"We'll be salting and plowing, trying to get at the compacted ice," he said. "Our plows handle snow very well, because that's what they were designed to do. But they weren't designed to plow ice."

Hunt said Saturday and Sunday are expected to be mostly sunny, and that should help the situation.

The storm prompted the National Park Service to close access to the popular mainland ice caves of the Apostle Islands National Lakeshore, which require visitors to cross Lake Superior ice in northern Wisconsin.

High winds and whiteout conditions Friday afternoon prevented the park service from checking lake ice conditions. But park rangers checked the ice Saturday morning, determined that it remained stable and reopened access to the caves.

More below-zero temperatures are on the way for the Twin Cities next week.

The weather service predicted a high of 11 on Monday and the single digits Tuesday and Wednesday, with lows near 10 below zero each day. Thursday is expected to be even colder, with a high of around zero and an overnight low of 15 below.